This invention concerns a cutting assembly and to related apparatuses such as a vehicle having such a cutting assembly mounted thereon. Such apparatuses are useful in the clearance of landmines and other unexploded ordnance.
As used herein the term xe2x80x9cordnancexe2x80x9d includes, but is not limited to, landmines, fragments of landmines, shells and fragments thereof, detonators, grenades and rockets.
Clearance of ordnance in general, and landmines in particular, is a subject that affects the lives of millions of people worldwide. It is well known that armies commonly lay thousands of mines at a time. This creates lethal minefields that often affect civilians more than they affect military personnel. The minefields usually remain highly hazardous to pedestrians and vehicles long after the cessation of armed conflict in an area.
The clearance of ordnance is a laborious process that presents serious risks to the individuals involved in it. The most commonly practised method of landmine clearance requires a pedestrian, protected by little more than a helmet and an armoured vest, repeatedly to prod at the ground with a rigid stick that is intended to locate unexploded ordnance by feel.
Aside from the risk of the individual accidentally treading on a mine during the clearance operation, this method is often unreliable for various reasons. These include that of variations in the depths to which the stick is inserted into the ground; and that the small contact area of the end of the stick, that is necessary for easy insertion of the stick into the ground, makes it easy to miss ordnance and leave it, unexploded, in the ground. Also, this method is difficult to practise in frozen ground. Freezing of the ground often hampers landmine clearance in the states formerly known as Yugoslavia, for example.
Patent application number EP-A-0 842 388 discloses an apparatus for detonating landmines.
The apparatus of EP-A-0 842 388 is highly effective in detonating landmines reliably and safely, but detonation alone does not render modern minefields safe. This is because the device of EP-A-0 842 388fails to detonate some mines, as a result of faults in the mines or the presence of unremoved safety devices; and some unexploded ordnance, hand grenades, mortars, shells, rockets, etc. Such devices are liable to cause death and injury to people who come into contact with them.
Many modern designs of landmine (such as anti-personnel mines manufactured from plastics materials) are intended to fragment on detonation into pieces that are perhaps 10%-50% of the size of an intact mine. It is known to use a flail machine, as an alternative to the apparatus of EP-A-0 842 888, for detonating ordnance. Sometimes the flail machine may fragment a mine without detonating it. This leads to the presence of comparatively large mine fragments, connected to operational detonators, in minefields supposedly rendered safe by the flail machine. Such pieces of landmine are highly explosive and remain capable of causing severe injuries to people who tread on or otherwise contact them.
Consequently the United Nations (UN), who have responsibility for many landmine clearance operations, have specified a requirement that clearance processes must be capable of reliably clearing all ordnance from contaminated areas. The UN have also specified that clearance should taken place to a depth of 25 cm where appropriate. However, there are certain areas, in the Falkland Islands for instance, where it may be necessary to clear to depths up to 50 cm.
It is thought desirable that landmine clearance processes must be capable of reliably reducing the size of each piece of ordnance, remaining in or on the ground after a clearance operation, to a maximum diameter of 10 mm. This ensures destruction of known detonators, for example.
Care needs to be taken during clearance that the topsoil and subsoils are not compacted or mixed in such a manner that the land is rendered infertile. This would cause hardship in the communities that landmine clearance is intended to benefit. In general landmines do not, naturally, sink below the topsoil. The depth of necessary clearance will however vary from one extreme, such as a rocky surface, to another, such as a peaty area in the Falkland Islands.
Thus it would be desirable to provide an apparatus for reliably removing and rendering safe all pieces of landmine in a minefield, regardless of their size and location, and regardless of the soil type.
According to a first aspect of the invention, there is provided a cutting assembly comprising a rotatable shaft supporting one or more elongate, arcuate blades, the or each blade having a base portion and a terminal portion remote from the base portion, the terminal portion being narrower than the base portion, the blade tapering in at least one plane between the base and terminal portions, a first, arcuate edge of the blade, extending between the base and terminal portions, being sharpened and the terminal portion including a second, sharpened edge, the or each blade protruding from the shaft with its terminal portion remote from the shaft and arranged so that the first edge of the or each blade is a leading edge when the shaft rotates in a predetermined direction, and the second sharpened edge trails the first edge during such rotation.
This arrangement may be lain on or inserted into the soil of a minefield or battle area and driven forwardly eg. by means of a pushing or pulling vehicle. Rotation of the shaft causes the first sharpened edge of the or each blade to cut through soil and eg. tree and plant roots, tripwires and cables, thereby freeing any unexploded ordnance such as mines. The trailing, second edge and the arcuate shape of the or each blade then lift such fragments, and other solid objects, to the surface of the minefield, from where they can readily be removed and destroyed or otherwise rendered harmless.
The action of bringing large fragments to the surface is also advantageous when the ground contains very large items of unexploded ordnance, such as complete mines. Such ordnance could damage the cutting assembly. The action of bringing such ordnance to the solid surface makes it visible, thereby permitting rendering the ordnance harmless in a controlled manner.
In preferred embodiments the first, sharpened edge (ie. the leading edge during use of the apparatus) is convexly curved. This assists in bringing solid matter to the surface of the minefield, without subsequently burying it again.
Preferably the cutting assembly includes a drive transferring means for imparting rotational motion to the shaft. Conveniently the assembly includes a support, for the rotatable shaft, that co-acts with one or more said first edges to sever scissile material carried on a said blade during rotation of the shaft. These arrangements allow the cutting assembly to cut through thick and/or tough members such as detonator wires, tripwires and plant matter such as branches and roots.
In preferred embodiments the cutting assembly includes a conveyor disposed adjacent the rotatable shaft and arranged to convey matter from a first location, adjacent the rotatable shaft, to a further location, remote from the rotatable shaft This feature permits the removal, from the vicinity of the shaft and blade(s), of unexploded ordnance, such as landmine fragments, and other solid matter that could cause injury in the event of an explosion nearby. Once removed from the vicinity of the rotatable shaft, the ordnance and other solid matter can be separated from one another and the ordnance rendered harmless.
Conveniently the conveyor is a bucket conveyor including a moveable belt having mounted thereon one or more conveying buckets. It is also preferable that the moveable belt is located and dimensioned so as to permit the or each conveying bucket when at the first location to receive matter cut by the said blade or blades on the shaft, and convey such matter to the further location.
In preferred embodiments the moveable belt is endless and is driven to move the or each conveying bucket between the first and further locations.
The foregoing features advantageously assist the conveyor to remove solid matter from the vicinity of the rotatable shaft and blade(s). In particularly preferred embodiments the conveyor is secured to follow immediately behind the shaft and blades when they are moving forwardly.
Preferably the or each carrying bucket includes a lip that, when the bucket lies adjacent the shaft, extends generally horizontally. This assists the carrying bucket to shovel the matter cut and loosened by the rotating blades. It is also preferable that the lip of the or each bucket is serrated. This feature allows the bucket(s) to pick up solid matter while permitting particulate matter, such as topsoil, to fall back to the ground and remain substantially in situ. Alternatively, parts of the bucket could be perforated to perform the same function.
It is of course desirable that the rotatable shaft, the blades, the support, the buckets and the conveyor are armoured, against detonation of unexploded ordnance and against shrapnel damage. This is advantageously achieved by manufacturing such components from, or including in their construction, blast-resisting materials.
According to a second aspect of the invention there is provided a moveable vehicle comprising a hopper open at one end and having therein one or more moveable grinding elements for grinding to a predetermined size matter conveyed into the hopper via the open end, the hopper including an outlet for ground matter, and the vehicle including operatively secured thereto a cutting assembly as defined herein for preparing grindable matter to be ground by the hopper.
Preferably the cutting assembly is demountably secured to the vehicle. This advantageously permits ready repair and/or replacement of the cutting assembly and vehicle.
In preferred embodiments the vehicle includes an adjuster for adjusting the operative height of the cutter assembly. Typically the adjuster may be such as to permit controlled variation of the depth in soil to which the cutter operates to loosen unexploded ordnance, such as landmine fragments, and other solid matter. The adjuster may also optionally be configured to raise the cutter above ground level, thereby permitting it to clear eg. solid rock over which the vehicle passes.
When the cutting assembly includes a conveyor for conveying matter from a first location, adjacent the rotatable shaft, to a further location remote therefrom, the further location, to which the cutting assembly conveys matter, preferably is a receiving part of a further moveable conveyor substantially interconnecting the further location and the open end of the hopper, the cutting assembly being arranged to deposit matter at the receiving part of the further conveyor, for conveyance into the hopper for grinding.
Conveniently the further conveyor includes a sorter for removing magnetic items from the matter conveyed by the further conveyor.
The foregoing features advantageously permit separation of eg. ferrous shrapnel from the material being conveyed to the hopper. This is desirable because:
i) the shrapnel could cause injury if left in the vicinity of unexploded ordnance;
ii) the shrapnel may reduce the fertility of agricultural land constituting a minefield, if not removed therefrom;
iii) the shrapnel may damage some kinds of grinding mechanism if allowed to enter the hopper; and
iv) the shrapnel can give misleading results during a post-clearance minefield audit using conventional ordnance detecting apparatuses such as metal detectors or ground searching radar.
A preferred form of the sorter comprises one or more electromagnets reciprocable between an item attracting position, in which the or each electromagnet attracts magnetic items from the further conveyor to itself; and an item depositing position, remote from the further conveyor; a power source for the or each electromagnet; and a control circuit for selectively switching the or each electromagnet on and off in dependence on its position. Such a sorter is advantageously effective in removing magnetic material.
Conveniently the or each electromagnet is supported on a moveable belt capable of moving the or each electromagnet, and hence any items attracted thereto, in a direction divergent from the direction in which matter is conveyed by the further conveyor. This arrangement ensures that ferromagnetic items are conveyed safely to a location removed from the hopper.
Alternatively the sorter may include an AC field generator that generates a rotating field. An AC field will have differing effects on eg. aluminium and iron based metals. A rotating magnetic field can be used, according to a known effect, to move such metal types in mutually divergent directions.
In preferred embodiments the vehicle includes a receptacle for magnetic material removed from the further conveyor.
This advantageously prevents the magnetic items, that typically are of ferrous materials, from being redistributed on to the cleared minefields. This in turn reduces the risks of injury and pollution arising from the presence of the magnetic items.
Conveniently the vehicle includes a motor having one or more ground engaging members driveably connected to the motor, for providing powered motion of the vehicle. This advantageously allows the vehicle to be self propelled. Also the presence of the motor provides a so-called xe2x80x9cpower take offxe2x80x9d by means of which eg. the cutter may be powered. xe2x80x9cPower take offxe2x80x9d as used herein includes medical, hydraulic, electrical and pneumatic actuators, drives and drive-transferring components.
According to a third aspect of the invention, there is provided a blade comprising an elongate, arcuate member having a terminal portion of lesser width than a base portion, the blade tapering in width between the base portion and the terminal portion, at least a first edge of the blade, extending between the base and terminal portions, being sharpened, and the terminal portion including a second, sharpened edge.
This blade is particularly suitable for use in a cutter as defined herein; and as part of a grinder forming part of a vehicle as defined herein.
Preferably the blade includes a third, sharpened edge extending between the base and terminal portions. It is also preferable that the first and third, sharpened edges define the shape of the blade, in the plane in which the blade tapers; and optionally that the curvature of the blade occurs in substantially the same plane as that in which the blade tapers.
These features advantageously assist the blade to perform a combined cutting and loosening function when driven through soil.